Many materials and combinations of materials have been utilized as filtration media for fluid filters to remove solid or liquid particulate from fluid streams. Fluid filters are found in use in commercial spray booths such as commercial paint spray booths and, when so utilized, are known in the art as paint arrestors. The commercial paint spray booths utilize controlled airflow to direct overspray away from the article being painted. This overspray is then exhausted from the booth through a filtration system comprising paint arrestors.
The performance or capabilities of such fluid filters are generally judged according to three main criteria:                A) Particulate Removal Efficiency;        B) Holding Capacity; and        C) Pressure Drop.        
Particulate removal efficiency of a filter is the ability of the filter to capture and retain particulate. For example, with respect to paint arrestors, efficiency is a representation of the percentage of the total paint particles entrained in the air stream exiting the booth that are captured by the filter.
Holding capacity is the amount of particulate which can be retained by the filter before the pressure drop becomes so great that the filter must be cleaned or replaced. Typically the test is stopped at 0.5 in. water and this represents the point at which a filter is typically exchanged due to airflow restriction. Proper airflow through the paint spray booth prevents quality issues with the painted surface. Relative to paint arrestors, paint holding capacity is the weight of the paint particles, solubolized, suspended, or in aerosol form, that the filter has captured and held for the time period specified. Paint holding capacity thus is determinative of the effective life of a filter. When dealing with disposable paint arrestors, the effective life has a direct bearing on the overall costs to a paint spray booth operator. Also, testing of paint arrestors also frequently records the amount of “run off” of paint particles from a filter. For example, with a vertically arranged filter, the run off includes particles that impact the filter but are not captured by the filter due to, for example, vertical flow off the filter to an underlying surface as in a liquid drain facility. As the efficiency determination for a filter includes the relative amount of captured paint particles to those generated, any run off prior to the holding capacity being reached results in a lowered efficiency rating for a filter, and thus a desirable filter is one with little run-off.
Pressure drop for a given flow rate of fluid through the filter is utilized as a measure of the power required to move the fluid stream through the media. Thus, for paint arrestors, pressure drop, initial and final, is the pressure differential as measured in the air stream across the filter before loading and after loading with paint. Pressure drop can thus affect the airflow in the booth and the subsequent ability to remove overspray from the paint area.
Spray booths are used in a variety of industrial applications as in the application of paint to many different products. A number of different spray atomizing application techniques can be used in such spray booths or in other spray environments. One of these techniques is an air atomization technique wherein coating or paint particles are mixed with an air stream being ejected from a spray gun and the air stream is directed to the product being coated. Another spray application technique example is an airless atomization technique wherein the coating material is atomized and propelled by hydraulic pressure to the product being coated. Yet another spray application technique example is an electrostatic spraying technique. In a typical electrostatic setting, the product to be coated is grounded and the coating material is atomized (either by an air or airless technique) and is electrically charged. As a result, the coating materials are deposited on the product due to the electrical attraction of charged coating particles to the product being coated.
Regardless of the spray technique that is used, a paint spray booth is commonly employed to contain, for example, evaporating solvents and to capture airborne atomized paint particles to minimize their impact on the environment and to protect painters from being unnecessarily exposed to the solvents and paint particles used in the coating process, particularly those that may be toxic. In fact, the use of spray booths is normally required for most liquid paint spray applications by federal or state regulatory agencies, including, in particular, the U.S. Environmental Protection Agency. Moreover, spray booths tend to enhance the quality of the finish being applied to a product being coated by providing a clean environment for the application of liquid coatings to these products.
In such spray booths, it is desirable to maintain a consistent, steady and uniform flow of air throughout the booth. Among other things, the consistent air flow prevents the accumulation of partially dried overspray on an object being coated so that the appearance of the object is not marred and tends to assist in providing the product with a quality finish. Moreover, spray booths prevent the accumulation of hazardous concentrations of potentially explosive solvent vapors. In fact, environmental clean air standards require that the emissions from spray booths must not include more than certain levels of particulates.
To remove paint particulates from the air being exhausted from a spray booth, a common practice is to employ a replaceable fibrous filter which will trap the majority of these paint particulates. These filters soon become clogged with such particulates so that the air flow through the spray booth tends to be substantially reduced, thus decreasing the air flow past the worker inside the booth and the products being coated. Moreover, the spray booth has to be shut down to replace such clogged filters (once per eight hour shift is not uncommon).
Typical paint arrestors or paint filters utilize flat or two dimensional surfaced sheets of non-woven fiber media. These filters can have laminated scrims, varying densities within the filters, and layers of various non-wovens of different constructions and appearances (e.g., see U.S. Pat. No. 6,231,646 to Schweizer et al.). In some cases, multiple filters of various constructions are used in series. High efficiency final filters can be pleated or sewn into bags to increase surface area, in an effort to lower pressure drop while maintaining higher efficiencies. In many paint spray booths, initial filtration is accomplished using flat sheets of non-wovens of various thicknesses. Expanded papers or laminated non-wovens that are slit and stretched producing voids (commonly referred to as paint pockets), can be added to the flat sheets in an effort to facilitate higher efficiencies and paint holding capacities.
There is utilized in the art disposable fluid filters comprised of a batting of, non-woven, fibrous, fluid material having surface patterns on a fluid contact surface. Examples are found in, for example, U.S. Publication No. 2006/0000196, U.S. Pat. No. 4,007,745 to Randall et al. and U.S. Pat. No. 5,658,641 to Berrigen et al. While U.S. Publication No. 2006/0000196 fails to describe how its filter is formed, each of U.S. '745 and U.S. '641 feature a compression technique wherein the fiber media is fed through a pair of comparison rollers to form a surface pattern on one side of the compressed batting (e.g., U.S. '745 involves a heated patterned roll; while U.S. '641 features one of the two compression rollers traveling at a high speed to form wrinkle indulations in the filter surface).
U.S. Pat. No. 6,071,419 describes first and second fluid permeable layers of non-woven fiber batting with the upstream layer formed with paint pockets as by a slit and stretch technique.
U.S. Pat. Nos. 6,740,610 and 6,500,292 describe a non-woven fiber pad for use in futons, mattresses, upholstery and the like having a convoluted surface formed by cutting a non-woven fiber batt having a plurality of low melt synthetic fibers. The non-woven batt is compressed generally toward a cutting device by a pair of counter-rotating drums having convoluted surfaces. A heated wire cutter is preferably utilized to form the desired contour pattern (reference is made to band saw use as an alternative in the '292 patent). The requirements associated with a comfortable futon or the like (e.g., a smooth skin surface due to surface fusing) are considered far removed from the characteristics associated with a filter such as a paint arrestor as explained in greater detail below.
U.S. Pat. No. 4,772,443 describes a fluid filter formed by manufacturing randomly disposed structure fibers and a thermoplastic binder fiber. The interstices between the fibers are fixed by applying a latex resin to the batting which is described as fixing the pore sizes of the filtering media before the filtering media is molded into the desired shape.
U.S. Pat. No. 6,159,258 discloses air filter elements of foam with an upstream surface area of peaks and valleys.
U.S. Pat. No 4,603,445 to Spann describes convolution assemblies used for contouring foam pads for cushioning purposes. As described in Spann, a convolution machine cuts a single piece of foam into two complementary pieces with contoured surfaces generated by the convoluter cut. The cut is done via a horizontal band saw, usually a smooth, practically continuously honed blade with a wedge shaped support. The resilient material is fed into the convoluter, and is compressed in a defined manner, based on the “tooling”. This tooling is assembled on two driven rollers that run parallel and on either side of the convoluter-cutting blade. As the rollers turn, the foam pad is fed into the machine, compressed by the tooling, and cut in the compressed state by the convoluter blade. As the cut resilient material recovers from the compression provided by the convoluter tooling, a contoured cut surface is formed on each separated foam sheet with the three dimensional pattern depending on the design of the tooling (e.g., the formation of sinuous or wave-like ridges). In general, convolution patterns are designed such that the two resultant products obtained are of the same mass, although this does not necessarily have to be the case.
While convoluting foam provides relatively consistent product output each time when the other factors associated with the foam material are maintained consistent, the inventors have determined that there is difficulties associated with convoluting non-woven material in an effort to provide filter media. That is, while a convoluted non-woven fiber layer may be well suited for inclusion within a mattress or the like, it may not be deemed commercially viable for filtering (e.g. a paint arrestor) as there are additional criteria involved with making a commercially viable non-woven fiber filter for use in a setting such as a paint spray booth. In other words, a non-woven fiber material such as one used for a mattress, can have varying density levels throughout its thickness and across its surface due to the fiber recipe characteristics and/or the formation process without being considered non-workable. Further, a high loft fiber composition best suited for cushioning and bedding material is able to have different characteristics than that used in the formation of a suitable filter for paint arresting as there is not the level of concern for consistency and surface integrity. Also convoluting non-woven (particularly high loft non-woven material) also presents the additional problem of inconsistent surface cutting results and/or a change in the media characteristics at the cut surface (e.g., a fraying of fiber ends or tearing of surface sections). Also, for many filter uses, it is preferable to have a convoluter that utilizes a non-heated material cutting device as, while a heated cutter can avoid some of the issues of tearing and fraying, for many fiber batt compositions it would alter the initial fluid impact surface of the filter and lessen the penetration potential of the filter and hence its holding capacity, etc.
While non-woven batting is relatively inexpensive and thus good for disposable use, it is prone to poor surface projection integrity (e.g., peak integrity). Attempts by the inventors to convolute fiber blends has resulted in peaks which were torn more than cut in the convoluting process. The peaks were also very fragile with loose fibers hanging or laying on top of the peaks. Also, subsequent handling of the convoluted high loft non-woven product resulted in further degradation of the projections or peaks. Loose fibers are deemed problematic when the filter is intended for use as a paint filter. This is because loose fibers introduce the potential for fibers to find their way into the booth and on the object being painted.
In addition, while convoluting foam material in a production setting is relatively straightforward due to the material involved (e.g., polyurethane foam), the processing of convoluted fiber in a production setting directed at filter usage is much more difficult in view of the different characteristics of the material involved, the interplay of that material with a convoluter equipment, and the end production characteristics required. For example, the inventors efforts involved in convoluting high loft, non-woven filter material has shown that high-loft recipes and surface patterns play a role in the resultant filter characteristics.
For example, an improper fiber recipe (fiber blend or mixture and/or fiber bonding means utilized) and/or an improper cutting technique and/or an improper surface pattern can lead to problems such as ill-defined pattern generation both within a single convoluted piece as well as between convolution runs for what is considered the same starting material. Additionally, inventor testing has determined that, in addition to fiber blend recipes playing a role in whether a convoluted end product is suitable for an end use in, for example, a paint spray booth application, the surface pattern itself can play a role both in removal efficiency and in product acceptability. That is, the nature of high loft, non-woven material is such that during, for example, a peak/valley convolution processing, there resulted in many inconsistencies relative to peak height, base thickness, peak definition, peak and base height ratios, etc.